Many power supplies for plasma chambers include an output filter stage that consists of energy storing components such as inductors and capacitors. These output filter stages are often used to, for example, reduce ripple in an output voltage of the power supply. If a plasma arc occurs within a plasma chamber that is receiving power from a power supply of this type, energy can be circulated within the energy storing components of the power supply for a period of time using a shunt switch in order to extinguish the plasma arc. After the plasma arc is extinguished, however, the energy circulated within the power supply can cause, for example, an over-voltage condition that can damage the power supply and/or plasma chamber if the energy is released to the plasma chamber.
Many types of over-voltage protection circuits have been used in power supplies to protect the power supply and/or plasma chamber from an over-voltage condition after a plasma arc has been extinguished. Some simple over-voltage protection circuit designs include passive components such as RC snubber circuits, transient voltage suppressor circuits, or metal oxide varistors that are used to dissipate energy. But many of these components must be large to handle the large number of plasma arcs that can occur, and the energy associated with one or more plasma arcs is dissipated rather than used by the power supply. Although some circuits can be designed to use the energy associated with a plasma arc by transferring the energy back to an input bus of the power supply, these designs are often quite complex and expensive. In other words, many current power supply designs are functional but are either too complex, expensive and/or inefficient. Accordingly, methods and apparatus are needed to address the shortfalls of present technology and to provide other new and innovative features. Accordingly, there is a need for improved plasma chamber power supply over-voltage protection methods and apparatus.